1. Field of the Invention
The present invention is directed to a multi-side shelter that may assume a collapsed configuration or an erected configuration. In particular, the present invention is directed to a truss that may assume a collapsed configuration or an erected configuration, and that may be used in a shelter.
Providing a shelter for protection from an ambient environment is generally considered a basic necessity. Traditionally, a shelter requires a substantial amount of time to construct, and is not easily moved from its construction site. However, there has arisen the need in special circumstances to provide a shelter that is readily transportable to a site, and that can be quickly set-up. Often, these shelters are intended to satisfy a temporary need, therefore these shelters must also be able to be quickly taken-down. Thus, it is also desirable for these shelters to be light enough to be easily moved, and durable enough to be reused many times.
2. Description of Related Art
Shelters for these special circumstances are typically constructed from a plurality of bars pivotally connected to one another so as to form a number of cooperative linkages that may assume a collapsed configuration and an erected configuration. In the erected configuration, a flexible sheet material is placed over the linkages so as to form a barrier between the ambient environment and the interior volume to be protected by the shelter.
A number of the convention shelters use linkages that are commonly known as lazy-tong type linkages. Alternatively, these linkages are also referred to as scissors or X-shaped linkages. A lazy-tong linkage includes at least one pair of bars that are pivotally connected at a common point along the length of each bar. In operation, first ends and second ends of each bar are respectively located relatively proximate to one another in a first configuration. In a second configuration, the bars are pivoted relative to one another about the common point such that the first end of each bar becomes relatively proximate to the respective second end of the other bar. Thus, reconfiguring a lazy-tong linkage reorients the greatest dimension of the pair of bars by 90.degree.. For example, if the bars of a lazy-tong linkage were initially oriented in a generally vertical configuration, operating the linkage would reorient the bars in a generally horizontal configuration.
In many conventional shelters, several lazy-tong linkages are successively joined by pivotally connecting two of the ends of one pair of bars to two of the ends of another pair of bars. The number of successively connected lazy-tong linkages generally corresponds to the ratio of the greatest dimension of the linkages in the erected configuration with respect to the greatest dimension of the linkages in the collapsed configuration. For example, a truss including three successively connected lazy-tong linkages would be able to assume a horizontal length in the erected configuration that is approximately three times its vertical length in the collapsed configuration.
Examples of conventional shelters using lazy-tong linkages to assume collapsed and erected configurations include the following U.S. Patents: U.S. Pat. No. 5,632,293 to Carter; U.S. Pat. No. 5,632,292 to Carter; U.S. Pat. No. 5,511,572 to Carter; U.S. Pat. No. 5,490,533 to Carter; U.S. Pat. No. 4,607,656 to Carter; U.S. Pat. No. 4,156,433 to Beaulieu; U.S. Pat. No. 3,526,066 to Hagar et al.; U.S. Pat. No. 3,496,687 to Greenberg et al.; U.S. Pat. No. 3,375,624 to Mikulin; U.S. Pat. No. 3,335,815 to Oakes; U.S. Pat. No. 3,199,518 to Glidewell; U.S. Pat. No. 3,174,397 to Sanborn; U.S. Pat. No. 1,853,367 to Mace; U.S. Pat. No. 1,728,356 to Morgan; and U.S. Pat. No. 1,712,836 to Mills.
Additional examples of conventional shelters using lazy-tong linkages to assume collapsed and erected configurations include German Patent 1 434 526; Italian Patent 692885; Great Britain Patent 672,815; French Patent 823.693; and Great Britain Patent 198,803.
U.S. Pat. No. 684,130 to Taubert discloses a screen having upper and lower trusses that each include a plurality of lazy-tong linkages.
Such conventional trusses and shelters constructed using lazy-tong type linkages suffer from a number of disadvantages including concentrating stress forces at its weakest points. All bending, torsion and shear forces that are applied to a truss constructed of one or more lazy-tong linkages are concentrated at the common pivot point for the bars. Moreover, this common pivot point is often the weakest portion of each bar due to the holes or other connecting structures necessary to form the pivot mechanism per se.
Another disadvantage of such conventional trusses and shelters constructed using lazy-tong type linkages is the lack of an inherently balanced position. Specifically, there is no tendency for a lazy-tong linkage to assume a balanced configuration since the lazy-tong linkage is never fully extended. That is to say, the bars of the lazy-tong linkage may not assume a parallel relationship for various practical and theoretical reasons. From a practical standpoint, the pivotal connections at the ends of conventional lazy-tong linkages would obstruct one another unless the ends were modified to form a lap joint. However, a lazy-tong linkage using lap joints cannot be fully collapsed because of bodies of the bars would obstruct one another. From a theoretical standpoint, allowing the bars of a lazy-tong linkage to assume a parallel relationship prevents the linkage from carrying any loads acting transversely to the plane of the parallel bars. That is to say, parallel bars primarily carry only tensile or compressive loads acting along the axes of the bars.
Examples of other known shelters that do not use lazy-tong linkages to assume collapsed and erected configurations include U.S. Pat. No. 1,493,915 to Baker and U.S. Pat. No. 1,326,006 to Sterhardt. Both of these patents disclose connecting trusses having a singular element that spans between legs of the shelters. These known shelters suffer at least one of the same disadvantages as those of the conventional trusses in that the stress forces are concentrated at the connection points for the spanning element. Further, these known shelters require complicated locking arrangements to maintain the collapsed and/or erected configurations. Additionally, because only one element is used, the size, weight and/or cost of manufacturing the spanning element must necessarily be increased to carry the loads imposed thereon.